The present invention relating generally to traffic monitoring systems and more specifically, to weight in motion sensors in the monitoring system.
WIM sensors (Weigh in Motion) built into road surfaces were introduced about 10 years ago and have been in use ever since, especially in the USA. For pre-selection of overweight axles, considerable success has been reached in the last few years. A most promising strip-type sensor was the introduction of the quartz piezo WIM sensor as explained in U.S. Pat. No. 5,461,924. The measuring accuracies are not yet satisfactory, mainly due to dynamic induced vibrations by vehicles. Therefore, it is the object of the invention to additionally monitor tire pressures and/or "road knockers", which are defects due to faults in suspension.
The solid state design of the WIM sensors has not only excellent force measuring properties, but may also be used as a high precision switching design, as explained further on. This new sensor will, therefore, allow new and unique combinations of weigh measuring as well as of monitoring tire pressure and "road knockers". A future standard WIM station thus could also be used for measuring tire pressure as well as for a "road knockers" monitoring station.
The invention has the further advantage that existing WIM stations could be supplemented with additional equipment and software, with the feature of tire pressure monitoring as an important addition to an already existing WIM station.
A further supplement of additional sensors and computer capacity would result in a third capability that would allow to detect "road knockers". The possibility to grade up existing WIM stations in one or two steps toward higher monitoring capability is an economic feature of the invention. Since WIM stations belong to the state of the art, the invention concentrates now on
tire pressure monitoring PA1 "road knockers" monitoring PA1 combinations with well known "Weigh in Motion" monitoring, PA1 full load PA1 half load PA1 wheel axle and total weight PA1 too low or too high tire air pressure PA1 defect suspension systems. PA1 tire air pressure faults PA1 road knocking faults
bringing thus the state of traffic monitoring onto a considerable higher level. These additional steps are possible with the same quartz piezo sensors as will be explained later.
1. Some explanations on Tire Pressure Monitoring
It is a well known fact that busses, trucks and other heavy road vehicles can be safely driven at highway speed only when all tires operate under normal tire pressure. Statistics in Great Britain revealed that .apprxeq.16% of heavy accidents were due to improper tire pressure.
There are many reasons for under or over pressure in tires. Once the vehicle is on the move, additional reasons may contribute to changes in the tire pressure. Therefore, without a built in tire pressure control system, the driver has no information available to him for adequate detection of this facet and, consequently, in this regard the safety of his vehicle is not within his complete control.
It is another well known fact that tires with overpressure reduce rolling resistance and thus reduce fuel consumption. There are also special high pressure tires on the market, however, in many States these "railroaders" are allowed only in the cold season, as they may cause heavy damage to the road during the summer season, with possible grooving of the softened asphalt.
The art of tire pressure measurement in motion, TPM, is still in the research state and nothing has been published by experimental stations. The reason for this is to be found in the complexity of the problems involved. No useful sensors have yet emerged, and visual methods cannot be considered. A main and simple parameter of the amount of air pressure in a loaded tire is its print length L, the length of the tire contact area. The measurement of this parameter, the presentation and evaluation of its results will be a part of this invention.
In order to simplify the problems, consideration will be given only to heavy-load vehicles, like busses and trucks, driving at highway speed. These vehicles must have similar wheel diameters and tires and thus will be the No 1 category. A further category, for instance with smaller wheels, would be category No. 2 and would need one,two or more additional sensors mounted in correspondingly different distances.
With this simplification of the No 1 category, approx. 70 to 80% of heavy-load vehicles can be monitored within the limits:
A too low air pressure B normal air pressure C too high air pressure
The axle load, of course, will have to be considered:
This will have a correctional influence.
Under these limitations, a collection of print lengths has to be set up, consisting of information given by the tire manufacturers as well as resulting from practical measurements. Statistical evaluations will reveal the important selection, Distances D.sub.2 and D.sub.3 of the sensors as will be explained further on.
The proposed monitoring system will consist of a pre-selection group of sensors and a selection group of sensors. The pre-selection group determines vehicle speed and axle weight in order to establish the load factor. The selection group of sensors separates the ##STR1##
The load factor will influence the tolerance limits by proper software compensation factors. The computer can distinguish the three basic forms of the evaluated curves immediately and can give the danger signal if only one of the up to 20 wheels of a vehicle, travelling at 80 miles/hour, has triggered the sensors signals.
The invention thus will detect in up to 90 to 95% of all cases the faulty vehicles and will direct them to a bypass station. Consequently, this will bring a considerable improvement in traffic safety and a reduction of road degradation.
2. Some Explanations to "Road Knocker" Monitoring
Another matter of concern and especially worrisome for operators of highways are the "road knockers", vehicles with defect suspension systems. Often such faults are not detected in normal service operations and occur mainly in certain speed ranges, in frequencies well above the basic vehicle vibrations. The knocking amplitudes of such random vibrations can reach up to +20% and more of the average static wheel load. This, therefore, is presenting a danger for blow-outs of tires and may destroy the road surfaces as well.
For traffic safety and road degradation reasons, it is thus most important to detect vehicles with defect suspension systems. No reliable detection system for such faults has so far been presented. This, however, will form the second part of this invention where methods are proposed on how to detect between 30 to 60% of "road knockers". With enlargement of the sensor base and with corresponding computer capacity, this percentage might be considerably improved.
The invention presents solutions for an optimal traffic monitoring system, consisting of means to monitor
All three monitored parameters are measured with the very same quartz piezo WIM sensors, arranged in different configurations. The invention will also cover parts of the ideal combination, like
and will, of course, also cover one or the other. Electronics and computer software will have to be separately adjusted to each solution and will not be treated here.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.